The present invention relates to a method for preparing an adipate ester or thioester. The invention further relates to a method for preparing adipic acid from said ester or thioester. Further the invention provides a number of methods for preparing an intermediate for said ester or thioester. Further the invention relates to a method for preparing 6-amino caproic acid (6-ACA), a method for preparing 5-formyl valeric acid (5-FVA), and a method for preparing caprolactam. Further, the invention relates to a host cell for use in a method according to the invention.
Adipic acid (hexanedioic acid) is inter alia used for the production of polyamide. Further, esters of adipic acid may be used in plasticisers, lubricants, solvent and in a variety of polyurethane resins. Other uses of adipic acid are as food acidulans, applications in adhesives, insecticides, tanning and dyeing. Known preparation methods include the oxidation of cyclohexanol or cyclohexanone or a mixture thereof (KA oil) with nitric acid.
Caprolactam is a lactam which may also be used for the production of polyamide, for instance nylon-6 or caprolactam-laurolactam copolymers (nylon-6,12). Various manners of preparing caprolactam from bulk chemicals are known in the art and include the preparation of caprolactam from cyclohexanone, toluene, phenol, cyclohexanol, benzene or cyclohexane.
The intermediate compounds, such as cyclohexanol, cyclohexanone or phenol, for preparing adipic acid or caprolactam are generally obtained from mineral oil. In view of a growing desire to prepare materials using more sustainable technology it would be desirable to provide a method wherein adipic acid or caprolactam is prepared from an intermediate compound that can be obtained from a biologically renewable source or at least from an intermediate compound that is converted into adipic acid or caprolactam using a biochemical method.
In U.S. Pat. No. 5,487,987, a method is described for the production of adipic acid, wherein use is made of a bacterial cell, wherein a carbon source is converted into 3-dehydroshikimate by the enzymes in the common pathway or aromatic amino acid biosynthesis of the bacterial cell, to produce cis, cis muconic acid, by the biocatalytic conversion of 3-dehydroshikimate. The cis, cis muconic acid is thereafter chemically reduced (using a platinum catalyst) to produce adipic acid. Thus, the final step requires chemical catalysis. It is further envisaged by the present inventors that the aromatic intermediates formed in the bacterial cell, may be toxic to the cell, likely requiring their concentration to be low in vivo as well as in the cell culture.
It is known to prepare caprolactam from 6-aminocaproic acid (6-ACA), e.g. as described in U.S. Pat. No. 6,194,572. As disclosed in WO 2005/068643, 6-ACA may be prepared biochemically by converting 6-aminohex-2-enoic acid (6-AHEA) in the presence of an enzyme having α,β-enoate reductase activity. The 6-AHEA may be prepared from lysine, e.g. biochemically or by pure chemical synthesis. Although 6-ACA can be prepared via the reduction of 6-AHEA by the methods disclosed in WO 2005/068643, the inventors have found that—under the reduction reaction conditions—6-AHEA may spontaneously and substantially irreversible cyclise to form an undesired side-product, notably β-homoproline. This cyclisation may be a bottleneck in the production of 6-ACA, and lead to a considerable loss in yield.